The prevalence of obesity in the United States has reached epidemic proportions and poses enormous public health challenges, as obesity is a major risk factor for type 2 diabetes, hypertension, cardiovascular disease and cancer, as well as an independent risk factor for mortality. Although diet and exercise are essential to weight management, it has become increasingly clear that a large proportion of patients would require drug treatment to decrease and maintain body weight. The goal of this grant is to understand the action of a novel cholesterol derivative with potent anti-obesity and anti-diabetic properties. MSI- 1436 is an aminosterol which we have found to cause reversible suppression of food intake, increased energy expenditure and normalization of glucose levels when administered by peripheral and more potently intracerebroventricular injection to rodents. Unlike other anorectics, a single injection of MSI-1436 produces a prolonged effect lasting several days. MSI- 1436 is effective in ob/ob and db/db mice, fa/fa rats, and diet-induced obese mice, suggesting that leptin signaling is not critical to its action. By contrast, MSI-1436 effect is blunted in agouti (Ay/a) mice, suggesting that its central action may involve the melanocortin pathway. Although acute MSI1436 administration strongly induces Fos-immunoreactivity in the paraventricular nucleus and to a lesser extent in the arcuate, ventromedial and pre-mammillary nuclei, the neuronal circuitry mediating the anti-obesity vs anti-diabetic effects of MSI-1436 is not known. We hypothesize that MSI-1436 enters the braii via a specific transport mechanism and engages hypothalamic neuronal targets to regulate energy balance and glucose homeostasis. Specific Aim 1 involves the injection of MSI-1436 into specific hypothalamic nuclei to determine which sites mediate the effects on feeding, body weight and glucose levels. Specific Aim 2 will analyze the distribution of MSI-1436 binding sites and determine the chemical phenotypes 01 MSI-1436 responsive neurons. Specific Aim 3 will determine the contribution of the central melanocortin system by analyzing MSI-1436 response in melanocortin receptor (MCR)-3 and 4 knockout mice. Finally, Specific Aim 4 will utilize GeneChip microarray to determine whether MSI-1436 regulates novel hypothalamic genes. Putative MS-1436 targets will be validated in multiple mouse models. Together these studies will provide insights into the mechanisms underlying MSI-1436 action in the brain. Understanding the basis for the novel effects of MSI-1436 on feeding behavior, body weight and glucose will greatly enhance the field of obesity and metabolism. New pathways affected by MSI-1436 may elucidate novel cellular targets for the treatment of obesity.